RonWessals Wrote:Pray, clarify? My understanding of a C-Flex, C-Flex+ and A-Flex setting of 3 means that the exhale pressure is reduced by 3 cmH2O, just like a ResMed EPR setting of 3. [ The timing of the pressure reduction cessation is different between the two, but the amount of pressure reduction is the same. ]
PR's description of the Flex systems can be found on the following PR webpages:
The critical thing in all
the descriptions is that Flex is variable
: The amount of pressure relief depends both on the Flex setting (1, 2, 3) AND on the user's individual exhalation effort for that particular breath. The following figure is the one for A-Flex:
The top curve represents the airflow into/out of the PAPer's lungs. The lower curve represents the pressure being delivered by the machine.
Notice that the pressure relief is NOT constant from breath to breath the way it is in the Resmed EPR system. The stronger the exhale, the more relief there is. In other words, the drop in pressure at the very beginning of the exhalation is proportional to the force of the exhale; it is NOT a reduction by a fixed amount of pressure.
The top humps on the pressure curve represent the current pressure setting
. In A-Flex and C-Flex+ the pressure relief is done in two stages: There's the initial (more significant) drop at the start of the exhale and then the pressure is increased part way
back to the current pressure setting for the rest of the exhale, with the pressure increasing all the way to the full (current) pressure setting at or near the beginning of the inhalation.
We can get a sense of the vertical scale on this graph when we note that the PR System One's Auto algorithm typically increases the pressure in increments of 0.5-1.0 cm units. Hence the vertical difference between top of the humps on the pressure curve are probably about 0.5-1.0 cm apart. Conveniently, the pair of dotted lines in the middle of that second graph are about the same distance apart as the top of the humps are. Hence that vertical distance most likely represents a difference of somewhere between 0.5-1.0 cm of pressure at most. And hence all settings of A-Flex (and C-Flex+) seem to deliver the same fixed
amount of pressure relief during the second half of the exhale, and that amount of pressure relief is probably between 1 and 2 cm. For simplicity's sake, let's just assume that the pressure relief during the second half of the exhale is about 1.5 cm. The A-Flex (and C-Flex+) setting determines how much extra
pressure relief is provided at the beginning of the exhale. On a very strong exhale, there may be as much as 3 cm of relief, but on a weak exhale, the relief will only be about 1.5 cm of relief, even with A-Flex (and C-Flex+) set to 2 or 3.
C-Flex provides significantly less
pressure relief than either C-Flex+ or A-Flex does. The C-Flex pressure graph looks like this:
Notice that in C-Flex, the pressure returns to the full setting half way through the exhale. In other words, the only relief in C-Flex is the variable amount of relief provided at the beginning of the exhale. Since there is no scale on this graph, it is difficult to accurately judge the actual amount of pressure relief. But it is clear that the relief provided by C-Flex = 3 is NOT three times as great as that provided by C-Flex = 1. Hence, even on the most forceful exhalations, we can conclude that C-Flex = 3 is not likely reducing the the pressure by 3 cm